A paracusia, or auditory hallucination,[1] is a form of hallucination that involves perceiving sounds without auditory stimulus.

A common form of auditory hallucination involves hearing one or more talking voices. This may be associated with psychotic disorders, and holds special significance in diagnosing these conditions.[2] However, individuals without any psychiatric disease whatsoever may hear voices.[3]

There are three main categories into which the hearing of talking voices often fall: a person hearing a voice speak one's thoughts, a person hearing one or more voices arguing, or a person hearing a voice narrating his/her own actions.[4] These three categories do not account for all types of auditory hallucinations.

In the past, the cause of auditory hallucinations was attributed to cognitive suppression by way of executive function failure of the fronto-parietal sulcus. Newer research has found that they coincide with the left superior temporal gyrus, suggesting that they are better attributed to speech misrepresentations.[8] It is assumed through research that the neural pathways involved in normal speech perception and production, which are lateralized to the left temporal lobe, also underlie auditory hallucinations.[8] Auditory hallucinations correspond with spontaneous neural activity of the left temporal lobe, and the subsequent primary auditory cortex. The perception of auditory hallucinations correspond to the experience of actual external hearing, despite the absence of physical acoustic output .[9]

Robert Schumann, a famous music composer, spent the end of his life experiencing auditory hallucinations. Schumann’s diaries state that he suffered perpetually from imagining that he had the note A5 sounding in his ears. The musical hallucinations became increasingly complex. One night he claimed to have been visited by the ghost of Schubert and wrote down the music that he was hearing. Thereafter, he began making claims that he could hear an angelic choir singing to him. As his condition worsened, the angelic voices developed into demonic ones.[10]

Brian Wilson, songwriter and co-founder of the Beach Boys, has schizoaffective disorder that presents itself in the form of disembodied voices.[11] They formed a major component of Bill Pohlad's Love & Mercy (2014), a biographical film which depicts Wilson's hallucinations as a source of musical inspiration,[12] constructing songs that were partly designed to converse with them.[13] Wilson has said of the voices: "Mostly [they're] derogatory. Some of it's cheerful. Most of it isn't."[14] To combat them, his psychiatrist advised that he "talk humorously to them", which he says has helped "a little bit".[11]

The onset of delusional thinking is most often described as being gradual and insidious. Patients have described an interest in psychic phenomena progressing to increasingly unusual preoccupations and then to bizarre beliefs "in which I believed wholeheartedly". One author wrote of their hallucinations: "they deceive, derange and force me into a world of crippling paranoia". In many cases, the delusional beliefs could be seen as fairly rational explanations for abnormal experiences: "I increasingly heard voices (which I'd always call ‘loud thoughts’)... I concluded that other people were putting these loud thoughts into my head".[15] Some cases have been described as an "auditory ransom note".

In the ancient world, auditory hallucinations were often viewed as either a gift or curse by God, or the gods (depending on the specific culture). According to the Greek historian Plutarch, during the reign of Tiberius (A.D. 14–37), a sailor named Thamus heard a voice cry out to him from across the water, "Thamus, are you there? When you reach Palodes, take care to proclaim that the great god Pan is dead."[16][10] The oracles of ancient Greece were known to experience auditory hallucinations while breathing in certain neurologically active vapors (such as the smoke from bay leaves), while the more pervasive delusions and symptomology were often viewed as possession by demonic forces as punishment for misdeeds.[10]

Treatment in the ancient world is ill documented, but there are some cases of therapeutics being used to attempt treatment, while the common treatment was sacrifice and prayer in an attempt to placate the gods. During the Middle Ages, those with auditory hallucinations were sometimes subjected to trepanning or trial as a witch.[10] In other cases of extreme symptomatology, individuals were seen as being reduced to animals by a curse; these individuals were either left on the streets or imprisoned in insane asylums. It was the latter response that eventually led to modern psychiatric hospitals.[17]

Auditory hallucinations were rethought during the enlightenment. As a result, the predominant theory in the western world beginning in the late 18th century was that auditory hallucinations were the result of a disease in the brain (e.g. mania), and treated as such.[17]

There were no effective treatments for hallucinations at this time. Conventional thought was that clean food, water, and air would allow the body to heal itself (Sanatorium). Beginning in the 16th century Insane Asylums were first introduced in order to remove “the mad dogs” from the streets and left them chained to walls and living in their own filth.[17] These asylums acted as prisons until the late 18th century. This is when doctors began the attempt to treat patients. Often attending doctors would douse patients in cold water, starve them, or spin patients on a wheel. Soon, this gave way to brain specific treatments with the most famous examples including Lobotomies, shock therapy and branding the skull with hot iron.[17]

However, numerous persons surveyed reported no diagnosis. In his popular 2012 book Hallucinations, neurologist Oliver Sacks describes voice hearing in patients with a wide variety of medical conditions, as well as his own personal experience of hearing voices.

In the case of psychotic patients the premier cause of auditory hallucinations is schizophrenia. In schizophrenia, patients show a consistent increase in activity of the thalamic and strietal subcortical nuclei, hypothalamus, and paralimbic regions; confirmed via PET scan and fMRI.[19][20] Other research shows an enlargement of temporal white matter, frontal gray matter, and temporal gray matter volumes (those areas crucial to both inner and outer speech) when compared to control patients.[21][22] This implies both functional and structural abnormalities in the brain, both of which may have a genetic component, can induce auditory hallucinations.[23]

Auditory hallucinations attributed to an external source, rather than internal, are considered the defining factor for the diagnoses of schizophrenia. The voices heard are generally destructive and emotive, adding to the state of artificial reality and disorientation seen in psychotic patients.[8] The causal basis of hallucinations has been explored on the cellular receptor level. The glutamate hypothesis, proposed as possible cause for schizophrenia, may also have implications in auditory hallucinations, which are suspected to be triggered by altered gultamatergic transmission.[24]

Studies using dichotic listening methods suggest that Schizophrenic patients have major deficits in the functioning of the left temporal lobe by showing that patients do not generally exhibit what is a functionally normal right ear advantage.[25] Inhibitory control of hallucinations in patients have been shown to involve failure of top-down regulation of resting-state networks and up-regulation of effort networks, further impeding normal cognitive functioning.[26]

Mood disorders have also been known to correlate with auditory hallucinations, but tend to be milder than their psychosis induced counterpart. Auditory hallucinations are a relatively common sequelae of Major Neurocognitive Disorders (formerly dementia) such as Alzheimer's disease.[27]

Auditory hallucinations have been known to manifest as a result of intense stress, sleep deprivation, drug use, and errors in development of proper psychological processes.[clarification needed][28] Genetic correlation has been identified with auditory hallucinations,[29] but most work with non-psychotic causes of auditory hallucinations is still ongoing.[28][30]

High caffeine consumption has been linked to an increase in the likelihood of experiencing auditory hallucinations. A study conducted by the La Trobe University School of Psychological Sciences revealed that as few as five cups of coffee a day could trigger the phenomenon.[31]

The primary means of treating auditory hallucinations is antipsychotic medications which affect dopamine metabolism. If the primary diagnosis is a mood disorder (with psychotic features), adjunctive medications are often used (e.g., antidepressants or mood stabilizers). These medical approaches may allow the person to function normally but are not a cure as they do not eradicate the underlying thought disorder.[32]

Cognitive behavioral therapy has been shown to help decrease the frequency and distressfulness of auditory hallucinations, particularly when other psychotic symptoms were presenting.[33] Enhanced Supportive Therapy has been shown to reduce the frequency of auditory hallucinations, the violent resistance the patient displayed towards said hallucinations, and an overall decrease in the perceived malignancy of the hallucinations.[33] Other cognitive and behavioral therapies have been used with mixed success.[34][35]

In recent years, repetitive transcranial magnetic stimulation (rTMS) has been studied as a biological method of treatment for auditory hallucinations. rTMS plays a role in altering neural activity over language cortical regions. Studies have shown that when rTMS is used as an adjunct to antipsychotic medication in treatment-resistant cases, the frequency and severity of auditory hallucinations can be reduced.[36]

There is on-going research that supports the prevalence of auditory hallucinations, with a lack of other conventional psychotic symptoms (such as delusions, or paranoia), particularly in pre-pubertal children.[37] These studies indicate a remarkably high percentage of children (up to 14% of the population sampled[38]) experienced sounds or voices without any external cause, although "sounds" are not considered by psychiatrists to be examples of auditory hallucinations. Differentating actual auditory hallucinations from "sounds" or a normal internal dialogue is important since the latter phenomena are not indicative of mental illness.

To explore the auditory hallucinations in schizophrenia, experimental neurocognitive use approaches such as dichotic listening, structural fMRI, and functional fMRI. Together, they allow insight into how the brain reacts to auditory stimulus, be it external or internal. Such methods allowed researchers to find a correlation between decreased gray matter of the left temporal lobe and difficulties in processing external sound stimulus in hallucinating patients.[8]

Functional neuroimaging has shown increased blood and oxygen flow to speech related areas of the left temporal lobe, including Broca’s area and the thalamus.[8]

It is suspected that deficits in the left temporal lobe attribute that lead to spontaneous neural activity cause speech misrepresentations that account for auditory hallucinations.[8]

Charles Fernyhough, of the University of Durham poses one theory among many but stands as a reasonable example of the literature. Given standing evidence towards involvement of the inner voice in auditory hallucinations,[39] he proposes two alternative hypotheses on the origins of auditory hallucinations in the non-psychotic. They both rely on an understanding of the internalization process of the inner voice.[28][38][40]

The internalization process of the inner voice is the process of creating an inner voice during early childhood, and can be separated into four distinct levels.[28][38][40]

Level one (external dialogue) involves the capacity to maintain an external dialogue with another person, i.e. a toddler talking with their parent(s).

Level two (private speech) involves the capacity to maintain a private external dialogue, as seen in children voicing the actions of play using dolls or other toys, or someone talking to themselves while repeating something they had written down.

Level three (expanded inner speech) is the first internal level in speech. This involves the capacity to carry out internal monologues, as seen in reading to oneself, or going over a list silently.

Level four (condensed inner speech) is the final level in the internalization process. It involves the capacity to think in terms of pure meaning without the need to put thoughts into words in order to grasp the meaning of the thought.

A disruption could occur during the normal process of internalizing one's inner voice, where the individual would not interpret their own voice as belonging to them; a problem that would be interpreted as level one to level four error.[28][38][40]

Alternatively, the disruption could occur during the process of re-externalizing one's inner voice, resulting in an apparent second voice that seems alien to the individual; a problem that would be interpreted as a level four to level one error.[28][38][40]

Psychopharmacological treatments include anti-psychotic medications. Psychology research shows that first step in treatment is for the patient to realize that the voices they hear are creation of their own mind. This realization is argued to allow patients to reclaim a measure of control over their lives. Some additional psychological interventions might allow for the process of controlling these phenomena of auditory hallucinations but more research is needed.[28]